This paper deals with the identification of the dislocation mechanisms involved during creep of a 2650-Al(CuMg) alloy. The dislocation microstructure has been studied by Transmission Electron Microscopy (TEM). We focused first on creep tests performed at a relatively high temperature: T = 150degreesC under a 280 MPa load. We show that the thermal activation has a double softening effect: it promotes cross-slip events on the dislocations and the subsequent precipitates bypassing and it activates the {001} non compact glide therefore giving a third degree of freedom to dislocations. Moreover the different creep stages seen to be controlled by the same dislocation mechanism, and the acceleration of the strain rate in the tertiary stage could be associated with dislocation multiplication events. Creep tests performed at the same temperature but at lower loads (200 and 220 MPa) reveal a lower cross-slip activity that could explain why the minimum strain rate reached during the creep tests is roughly 30 times lower than at 280 MPa.